Behavioral aspects of reproductive senescence in aging female rats will be investigated utilizing observational techniques in a longitudinal design. Circadian and estrus patterns in food intake, sexual receptivity, and locomotor activity will be the principal dependent measures. Alterations in estrus cyclicity peculiar to transitional periods between normal estrus cycling and constant estrus or recurrent pseudopregnancy will be examined and the degree to which they predict the time of occurrence and/or type of senile estrus deviation will be determined. Measures of behavioral cyclicity following treatments known to cause premature appearance of senile estrus deviations (early hemiovariectomy) or produce similar syndromes (constant illumination) will be compared to those observed during normal aging. In parallel fashion behavioral aspects of the estrus cycling induced in aging rats by hormonal or pharmacological treatment will also be examined and compared to young, normally cycling animals. Age differences in the sensitivity of food intake, sexual receptivity, and locomotor activity will be examined as will the relationship between the response to standard doses of estradiol and the fluctuations of these behaviors during the normal estrus cycle. Lastly, the estrus fluctuations in behavior will be related to plasma levels of ovarian steroids in rats of different ages.